1. Field of the Invention
The present invention relates to a microphone apparatus, and more particularly to an acoustic structure, which is applied to a radio apparatus, a recording apparatus and the like in which a microphone is built in a microphone case or a main housing, for resolving the problem in which clarity of voice information to be absorbed is lost by a phenomenon in which transmitting voice with a strong sound pressure or under strong wind, wind noise or prosodic features of voices based on various kinds of languages and individual differences are generated.
2. Description of the Related Art
Conventionally, in a mobile-use radio apparatus, a microphone is built in a microphone case, which is cable-connected to a main body. In a handy-type transceiver, a microphone is built in a housing.
In accordance with miniaturization and supersensitization of the microphone, there has been recently adopted a system wherein a small sound absorbing hole is formed on a microphone case or a housing panel and the microphone is held on the back thereof and a sound perceptible portion of the microphone is fixed to the sound absorbing hole to be opposed thereto in this manner.
However, in the apparatuses used outdoors such as the radio receiver and a transceiver, the following problems occur.
More specifically, a speaker must put one's mouth close to the sound absorbing hole and utter a loud voice. Moreover, since a strong current of air occurs along the front surface of the panel under the strong wind, a space, which is formed between the absorbing hole of the panel and the sound perceptible portion, functions as a column of air or a sound box and a so-called “wind noise” is inputted into the microphone, and this makes it difficult for a receiver side to hear the transmitting sound.
Furthermore, a linear sound guide channel is formed between the absorbing hole of the panel and the sound perceptible portion. Accordingly, when the speaker puts one's mouth close to the sound absorbing hole as mentioned above, a strong sound pressure caused by breath directly acts on the sound perceptible portion even in an unvoiced state and a breath sound is voice-outputted, thereby grating on a receiver's ear.
As measures against these problems, the following systems are adopted:
(1) A system in which a portion close to the sound absorbing hole of the panel surface is louvered and the current of air is scattered to prevent occurrence of resonance;
(2) A system in which a sponge or like is interposed between the sound absorbing hole and the sound perceptible portion to eliminate an element such as a column of air or the sound box in order to prevent the sound pressure caused by breath from being directly applied to the sound perceptible portion; and
(3) The size of the sound absorbing hole is formed as small as possible, and the sound guide channel is bent at the right angle twice to be guided to the sound perceptible portion of the microphone.
However, since various resonant conditions and sound pressure propagation conditions may be established depending on the state of the sound pressure caused by the uttered sound close to the panel surface and the direction of the wind, univocal louver formation as adopted in measures (1) cannot solve the aforementioned problems. In addition, it is almost impossible to form an ideal louver.
Measures (2) are substantially useful for the wind noise, breath sound and the like. However, this reduces sensitivity as a sound absorbing system and particularly attenuates high frequency components of voice frequency considerably, thereby deteriorating the reception quality on the receiver side.
Measures (3) are useful for the breath sound since the reduction in the sound absorbing hole lowers the sound absorbing efficiency. However, there is no effect on the wind noise since the sound guide channel functions as an element of the column of air.
In the radio apparatus used outdoors, conditions such as the state of noise, direction of the wind, wind force, and the like are frequently changed, and a microphone use environment is variously considered. It is naturally desired that high-quality transmission system be always maintained in any condition.
In addition, the voices represent a great variety of prosodic features based on kinds of languages such English, French, and so on and individual differences in pronunciation characteristics. There has been experimentally known a problem in which the transmission system does not match a voice with a specific prosodic feature and particularly consonants, which belong to the high frequency, become unclear. Microphone apparatuses that are adaptable to such individual circumstances are most desirable.
The aforementioned problems and demands are not limited to the radio apparatuses, and the same can be applied to the portable recording apparatuses.
In consideration of the aforementioned problems, it is an object of the present invention to provide a microphone apparatus, which can easily adjust a transmission system from a panel front surface side in response to circumstances, whereby making it possible to input a high quality voice having neither wind noise nor a breath sound generated and to implement the input of clear voice against various kinds of prosodic features of the voice.